Method for inhibiting reactive argillaceous formations and use thereof in a drilling fluid

ABSTRACT

The present invention relates to a method of stabilizing argillaceous rocks containing reactive clays in the presence of water, wherein said argillaceous rocks are placed in contact with an aqueous solution containing a polymer with hydrophilic groups and hydrophobic groups.

This application is a Divisional application of application Ser. No.122,540, filed Oct. 14, 1993 now abandoned.

The present invention relates to a method and its application to afluid, particularly a drilling fluid, said method being designed toinhibit highly reactive argillaceous formations in the presence ofwater. The method according to the invention consists in particular ofbringing the reactive formations in contact with an aqueous solutionincluding hydrophilic and hydrophobic polymers.

A hydrophobic substance is generally defined as being a nonpolar organicsubstance. A hydrophilic/hydrophobic polymer according to the presentinvention will be such that the balance between the hydrophilic andhydrophobic units causes this polymer to be water-soluble.

In the area of oil drilling, the problems raised by argillaceousformations are well known. When these formations are drilled usingwater-based drilling fluids, complex chemical reactions take placewithin the argillaceous structure by ion exchange and hydration. Thesereactions result in swelling, crumbling, or dispersion of clay particlesin the formation through which the drill passes. Problems also arise incontamination of the drilling fluid by clays, stability of the drillingwalls, and migration of fine clay particles contained in a reservoirrock.

In this application, we will use the term "argillaceous formations" todescribe geological formations with a certain proportion of clayparticles, which proportion can be very large or very small. In thefollowing, the usual abbreviations Hb and Hy will be used to designatehydrophobic and hydrophilic, respectively.

In the oil industry, the problems cited above have been solved inparticular by using nonaqueous drilling fluids. For example, by drillingwith air, but more commonly with a fluid whose continuous phase is basedon liquid hydrocarbon. However, drilling with these types of mud knownas "oil-type muds" has numerous drawbacks: prohibitive cost of fluid,toxicity, and above all pollution of wastes by the oil. Current wasteregulations call for treatment techniques and costs such that oil-typemud is often impossible to use.

In this case, the water-based fluids contain water-soluble polymers ableto provide a drilling fluid with the necessary characteristics, namely:sufficient viscosity to clean the well properly, and ability to reducethe filtrate and disperse the fine particles. However, these additivesare not satisfactory with regard to inhibition of clay swelling when theformations traversed have high reactivity, which is the case inparticular in the North Sea.

The systems currently in most widespread use are fluids includingpolymers and potassium ions. The polymers are often partially hydrolyzedpolyacrylamides and/or cationic polymers. These systems have frequentlybeen shown to be ineffective.

U.S. Pat. No. 4,299,710 discloses a drilling fluid composed of acombination in aqueous solution of thickeners such as a copolymer and apolysaccharide. Among other properties, this fluid has the property oflimiting clay swelling. However, the copolymer structure described has amolecular weight of at least 25×10⁴ daltons and there is no optimizationrelationship between the molecular weight and the length of thehydrophobic part. Moreover, it is a complex fluid whose characteristicsemerge from the combined effects of the products, and is particularlysuited for a drilling fluid with low solids content, particularly a lowcontent of clays.

The present invention relates to a method for stabilizing rockscontaining reactive clays in the presence of water. With this method,said argillaceous rocks are placed in contact with an aqueous solutioncontaining a polymer with hydrophilic groups (Hy) and hydrophobic groups(Hb). The groups are designed to inhibit swelling and/or dispersion ofsaid argillaceous rocks.

The hydrophobic groups contain between 1 and 30 alkyl groups, with themolecular proportion of said hydrophobic groups being between 5 and 60%,and said polymer has at least one of the following structures:

*Structure a) of the (Hb)--(hydrophilic chain Hy)--(Hb) type wherein thehydrophilic chain Hy is composed of a polyoxyethylene (or POE) chainwith the following general formula: ##STR1## where R₁ and R₂ are each:H, a C₁ -C₃₀ alkyl, aryl, or alkylaryl radical,

where a, b, and c may respectively assume the values of: 0 to 50, 0 to150, and 0 to 50, and (a+b+c) is not zero,

and in which the hydrophobic groups Hb are alkyl or alkyl-aryl chainsconnected to the hydrophilic chain Hy by groups containing at least oneurethane function with the following general formula: ##STR2## where R₃is H or a C₁ -C₃₀ alkyl radical, a cycloalkyl radical, a C₆ -C₃₀ phenylradical which may be substituted by one, two, or three C₁ -C₃₀ alkylradicals, or a fatty ester of the sorbitan type,

the molecular weight of said polymer is greater than 27,000 daltons.

*Structure b1) of the --(Hb)--(Hy)-- type with a statisticaldistribution, said structure b1) being a polyacrylamide derivativeresulting from copolymerization of acrylamide with a hydrophobiccomonomer, and wherein the hydrophilic group is acrylamide, possibly inthe form of acrylic acid, acrylate, or sulfonate according to thefollowing formula: ##STR3## where R₅ is H or CH₃ and Z₁ is COOH or CONH₂or CONHR"₁, R"₁ is a C₁ -C₃₀ substituted alkyl-, aryl-, oralkylarylsulfonate radical.

*Structure b2) of the --(Hb)--(Hy)-- type with a statisticaldistribution, said structure resulting from radical polymerization ofethylenic monomers containing carboxylic functions, particularly anacrylate/alkyl acrylate copolymer with the following formula: ##STR4##where x is between 0.4 and 0.8, M is H or Na or K or any othermonovalent ion, and where the length of the hydrophobic groups R₄ ischosen as a function of the molecular weight of the polymer according tothe following rules:

For a polymer with a molecular weight less than about 10⁵ daltons, R₄contains at least two carbon atoms,

For a polymer with a molecular weight between approximately 5×10⁵ and2.5×10⁶ daltons, R₄ contains at least four carbon atoms,

*Structure c) composed of a principal chain containing units withhydrophilic groups Hy and units with hydrophobic sidechains Hb,constituting a "comb-type" structure, said structure having partiallyesterified carboxylic acid groups whose hydrophilic ester groups are ofthe POE type, and units with a hydrophobic sidechain having thefollowing general formulas: ##STR5## where R is a hydrophobic chain andZ₄ is OH or (POE)R'₁, and the molecular weight is greater thanapproximately 20,000 daltons.

The polymer corresponding to Structure a) may have a hydrophilic chainHy with the form (CH₂ CH₂ O)_(b), where b is 1 to 150, a hydrophobicgroup Hb with the form CH₃ (CH₂)₁₁, or ##STR6## the groups with aurethane function joining Hb to Hy may be of the formula ##STR7##

The hydrophobic unit Hb with Structure b1) may have at least one of thefollowing forms:

N-alkylacrylamide, alkyl acrylate, N-substituted acrylamide, orsubstituted acrylate, whose substituted part is a nonionic surfactant,said hydrophobic unit having the following general formula: ##STR8##where R₅ is H or CH₃ and Z₂ is COOR₇, COOR'₁, CONR₁ R'₁ or CONR₁ R₇, R₇being a nonionic surfactant composed of an alkyl polyoxyethylene chainand R'₁ is a C₁ -C₃₀ alkyl, aryl, or alkylaryl radical.

Cationic units can be introduced into Structure b1), said units havingthe following general formula: ##STR9## where R₆ is H or CH₃, Z₃ is(CH₂)_(n), COO(CH₂)_(n) or CONH(CH₂)_(n) with n being a number from 0 to20, and Y is R₁ N⁺ R'₁ R₂ wherein only one of the three radicals may beH.

The polymer according to Structure b2) may have a value of approximately0.55 for x, R₄ may have four carbon atoms, and said polymer may have amolecular weight of between 5×10⁵ and 2.5×10⁶ daltons, preferablyapproximately 10⁶ daltons.

The polymer according to Structure b2) may have a value of 0.8 for x, R₄may have four carbon atoms, and said polymer may have a molecular weightof between 10⁴ and 5×10⁴ daltons, preferably approximately 17×10³daltons.

For the polymer with Structure c), R can be a C₁₂ to C₁₄ alkyl chain andZ₄ may be OH or (POE)_(m) CH₃, with m being from 6 to 10.

The method according to the above characteristics may involve an aqueoussolution with between 1 and 10 g/liter of hydrophilic and hydrophobicpolymer.

The invention also relates to a use of the above method with fluidscontacting reactive argillaceous formations, particularly fluids fordrilling, fracturing, cementing, well treatment, or assisted recovery.

Patents EP-0,398,576, GB-2,128,659, and EP-0,311,799 in particulardisclose polymers or fluids with hydrophobic groups, but none of themrelates to inhibition of clay swelling.

The basic idea of the present invention is to determine an optimizedstructure for a polymer having hydrophilic and hydrophobic groups. Themolecular weight must also be optimized as a function of the polymerstructure. This is because strong, dense adsorption of this polymer ontoargillaceous formations and a highly hydrophobic nature of the layer ofthis adsorbed polymer are some of the favorable conditions forcontrolled inhibition of the swelling of argillaceous formations.

One of the teachings of the present invention is the demonstration ofcertain parameters that allow the engineer to control theclay-inhibiting nature of a solution according to the invention.

The density of the polymer layer obtained by adsorption may be lowbecause the molecular weight is too low, but can be controlled, inparticular improved, by optimizing the structure of the polymer.

Likewise, a polymer with too high a molecular weight and too large aproportion of hydrophobic groups may, in certain tests, reveal a goodadsorption capacity, particularly to clays, provided the hydrophobicpolymer solution according to the invention is not circulated. It hasbeen found that the thickness of the adsorbed layer of certain polymers,not optimized in terms of molecular weight, proportion, and length ofhydrophobic chain, was partially destroyed by the dynamic testsimulating circulation of a drilling fluid. In this case, the inhibitingnature of such a solution is strongly affected.

The hydrophobic nature of the adsorbed polymer layer limits diffusion ofwater and ions of the aqueous solution thus inhibiting swelling and/ordispersion of argillaceous formations.

Moreover, it is found that a polymer corresponding to Structure b) hasvery good resistance to the usual contaminants, particularly calciumions, and to high temperatures.

Determination of the selected polymer has to do particularly andessentially with the choice of the best-suited structure, the mutualdistribution of the hydrophilic and hydrophobic groups, the molecularweight of the polymer obtained, and the nature of the various monomers.

In the present invention, the term "POE" corresponds to thepolyoxyethylene chain as defined by the structural formula given abovefor Structure a).

Reference may be made to the following article: "Polymers in AqueousMedia, Performance through Association", Ed. J. E. Glass, Advances inChemistry Series, No. 223, ACS 1989.

The hydrophilic/hydrophobic polymer solutions in the context of thisinvention are alkaline and may include other components designed toprovide the fluid containing this solution with other characteristicssuch as inhibition of swelling of rocks containing clays.

In this invention, the drilling fluids can contain, in aqueous solution,the hydrophilic and hydrophobic polymers described above in order toinhibit the swelling of rocks containing reactive clays that areencountered during drilling. These drilling fluids may in particular beconventional fluids with a colloid content, fluids with a low solidscontent, or polymer-based fluids.

In fact, this type of polymer presents practically no problems ofincompatibility in the presence of other additives generally used inparticular in drilling fluids.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be better understood and its characteristics will bebetter appreciated by reading the following experiments, which are notlimiting, illustrated in particular by the attached figures wherein:

FIG. 1 represents the swelling of a sample contacted by a polymeraccording to the invention,

FIG. 2 represents the temperature stability of a polymer according tothe invention,

FIG. 3 represents the stability over time of a polymer according to theinvention raised to 90° C.,

FIG. 4 represents the stability to calcium ions of a polymer accordingto the invention as a function of time,

FIG. 5 gives the results of a disaggregation test,

FIG. 6 shows a test cell schematically,

FIG. 7 gives the test results from the cell in FIG. 6,

FIG. 8 represents the water content of a sample tested in the cell as afunction of distance from the axis of the sample.

The properties and advantages of the polymer here called H3 aredemonstrated by the tests described below. The H3 structure is anacrylate/butyl acrylate copolymer containing substantially 20% molecularweight of butyl acrylate and has the following structural formula:##STR10## where R₄ is n-butyl and x=0.8.

The molecular weight of this polymer is essentially 17×10³ daltons.

The behavior of the H3 polymer is compared with a polymer called H6 thathas the same general formula but contains 45% molecular weight of butylacrylate. The H6 polymer has an x value of essentially 0.55 and amolecular weight of approximately 8×10⁶ daltons.

Another polymer called H1 is tested. The structure of H1 corresponds toStructure a) described above and has the following formulation:

hydrophilic part: (CH₂ CH₂ O)_(b) where b is between 1 and 150,

hydrophobic part: CH₃ (CH₂)₁₁,

urethane part joining Hb to Hy: ##STR11##

The molecular weight of this polymer is essentially 27,000 daltons.

A fourth polymer called H2 is tested. The structure of H2 follows Modelc) and has partially esterified carboxylic acid groups whose hydrophilicester groups can be of the POE type, and hydrophobic sidechain groups,with the following general formula: ##STR12## where R is a C₁₂ to C₁₄alkyl chain and Z₄ is OH or (POE)_(m) CH₃, and m is between 6 and 10.

The molecular weight can be greater than approximately 20,000 daltons.

All the solutions tested will be at essentially pH 8 and in the presenceof 5 g/liter of KCl except for Tests 0 and 5.

The polymer concentrations according to the invention are in the rangefrom 1 to 10 g/liter, more specifically approximately 6 g/liter forpolymers H6 and H3. The choice of these concentrations does not limitthe scope of the invention.

Test 0

To measure the extent of adsorption of the polymer according to theinvention, a Green Bond montmorillonite solution exchanged in thepotassium form and dispersed in the electrolyte considered is made tocontact a polymer solution in the same electrolyte.

The experimental conditions are: temperature 30° C., agitation at 10 rpmfor 24 hours, S/L (solid/liquid) ratio between 2×10⁻⁴ and 2×10⁻³.Because of autocoagulation and flocculation of the particles, themeasurements are extrapolated to S/L=0. This extrapolated valuecorresponds to the adsorption of the polymer expressed in milligrams pergram of argillaceous particles. In the presence of 0.1 g/liter of KCl,for a nonhydrolyzed polyacrylamide, H1, and H2, the values of 700, 540,and 200 mg/g respectively are obtained.

It will be recalled that the molecular weights of these polymers are10⁷, 27,000, and 20,000 daltons respectively.

Under the same testing conditions, a nonhydrolyzed polyacrylamide with amolecular weight of approximately 20,000 daltons is adsorbed atapproximately 70 mg/g and at approximately 600 mg/g for a molecularweight of approximately 10⁶ daltons. This is described by J. Y. Bottero,M. Bruant, and J. M. Cases in J. of Colloid and Interf. Sci.; 124, No.2, August 1988, 515-527.

At higher salinity, with approximately 10 g/liter of KCl, adsorption ofthe nonhydrolyzed polyacrylamide and H6 is 400 mg/g and 4300 mg/g,respectively.

Under the same conditions, adsorption of the H3 polymer is of the sameorder of magnitude as that of nonhydrolyzed polyacrylamide while theirmolecular weights are 17,000 and 10⁷ daltons, respectively.

This test shows the high adsorbability of the hydrophilic andhydrophobic polymers according to the invention on clays by comparisonto polyacrylamides with comparable molecular weights.

Test 1

To test the inhibiting power of the polymer according to the invention,a sample of Green Bond montmorillonite is placed in contact with asolution containing the polymer. The sample is in the form of a claycake compacted at a pressure of 100 to 1500 bars and containing 43%exchangeable calcium. The various cake samples used have activities ofbetween 0.5 and 0.98. The electrolyte used has an activity of between 1and 0.995. In this case the activities were measured with anelectrohygrometer made by the Novasina Company in Switzerland.

The experimental conditions are: temperature 30° C., solid/liquid volumeratio equal to 0.1, with gentle agitation and kinetics monitored over 24hours.

The results are shown in FIG. 1, with the activity aw of the sample onthe horizontal axis and the swelling G of the sample on the verticalaxis, given as percentages.

Line 11 connects the points corresponding to cake samples with differentactivities. It can be seen that the hydrophilic and hydrophobiccopolymer H3 is effective whatever the ratio between the activity of theelectrolyte and the activity of the Green Bond cake.

This result may be compared with the work of M. E. Chenevert describedby this author in "Shale Alteration by Water Adsorption" in the Journalof Petroleum Technology, September 1970 where he shows that to inhibitthe swelling of a clay, it is necessary to balance the activities of thewater in the drilling mud and the water in the clay. Thus far, the priorart has recommended balancing the activities or chemical potentials byadding sufficient quantities of salt to the mud, particularly potassiumchloride.

The method according to the invention, however, discloses that thegreater the imbalance of the activities, the greater is theeffectiveness of the H3 polymer by comparison to the partiallyhydrolyzed polyacrylamide tested under the same conditions. The resultsrepresented by Line 2 show that swelling of the samples is distinctlyhigher in the presence of polyacrylamide (Line 2) than in the presenceof H3 (Line 11) or H1 (12).

During the test, the swelling kinetics were monitored for 24 hours, andit was noted that the rate of swelling was low with hydrophobic polymerssuch as H3 and H1.

By comparison, and to offer some perspective, a cake sample similar tothe foregoing was broken up completely and dispersed due to swellingwhen immersed in a simple brine with 5 g/liter of KCl.

Test 2

One of the major drawbacks of the polymers known in the prior art istheir temperature instability. Hence, the method according to thepresent invention has the advantage of retaining good structuralstability at the temperatures conventionally encountered in oildrilling. If the hydrophilic and hydrophobic groups are altered, eitherin arrangement or in number, the inhibiting power of the solutionaccording to the invention may be greatly attenuated. FIG. 2 shows thechange in the viscosity of solutions of a polymer with a structureidentical to that of H6, but with a molecular weight equal to at least10⁶ daltons. The scale of polymer concentrations C is on the horizontalaxis and the reduced specific viscosity RSV on the vertical axis.Reduced specific viscosity is equal to (Eta_(r) -l)/c where Eta_(r) isrelative viscosity and c, concentration.

Line 3 represents the initial viscosity of the hydrophilic andhydrophobic polymer tested as a function of its concentration, at thetemperature of 30° C.

Lines 4 and 5 relate to the same polymer heated for 24 hours at 90° C.and 140° C. respectively in the presence of approximately 1 ppm ofoxygen.

We observe an increase in viscosity with temperature due essentially toan increase in hydrophobic interactions.

Infrared spectroscopy shows that the structure of the tested polymerremains stable so that its inhibiting power remains intact and similarto that at the beginning.

Comparatively, under the same testing conditions, it is found thatpartially (17%) hydrolyzed polyacrylamide hydrolyzes to about 60% andthe chain begins to break down. This test is not illustrated here.

Test 3

To confirm the stability of the polymer heated to 90° C., thetemperature was held for 48 hours and then up to 120 hours. Line 4' inFIG. 3 corresponds to 24 hours' heating. In this FIG. 3, the pointsrepresented by the crosses of the "13" type are obtained after 48 hours'heating and the points represented by the "14" type crosses, after 120hours. After 48 hours' heating, the viscosity is seen to increase nofurther since Line 6 connects all the types of cross.

Test 4

This test relates to the influence of calcium ions on the same polymer.FIG. 4 gives the RSV of the polymer under different solution conditions:

Line 7 is a polymer solution at a concentration of 6 g/liter with 5g/liter of KCl.

Line 8 is the previous solution to which 1 g/liter of CaCl₂ has beenadded.

Line 9 represents the previous solution after 36 hours.

Line 10 represents the previous solution after 15 days.

An increase in interactions of hydrophobic groups with each other overtime is observed; this is clear if we compare Lines 9 and 10,particularly their slopes.

High stability of the polymer tested is observed under these solutionconditions.

By comparison, a polyacrylamide that is 17% hydrolyzed precipitatesunder the same conditions and the solution viscosity decreases. This isshown in the work of J. Francois and T. Schwartz described in"Solubility Limits of Partially Hydrolyzed Polyacrylamides in thePresence of Divalent Ions," Macromol. Chem., 2775-2785, 1981, where wesee that the partially hydrolyzed polyacrylamides are stable only fordivalent cation concentrations well below 1 g/liter.

Moreover it is clear that the stability to calcium of the polymer testedis particularly good by comparison with the partially hydrolyzedpolyacrylamide since the calcium stability limits of the latter arerapidly reached in view of its substantial hydrolysis as a function oftemperature.

All the properties shown in Tests 2, 3, and 4 are attributed to thecharacteristics of the hydrophilic and hydrophobic polymers whatevertheir molecular weights. Indeed, it seems that inter- and intra-chaininteractions have a favorable effect on temperature stability and incase of contamination.

Test 5

This test describes the influence of the adsorbed polymer on thedisaggregation process of an argillaceous sample in the form of a cake.The cake is made from a clay rock called "Stone I" containingapproximately 50% clay. The rock is dispersed then recompacted at 8 T.The activity of the cake thus obtained is approximately 0.82. The testconsists of suspending the cake in a test solution. The solutions testedcontain no KCl. The cake crumbles over time and the quantity of claylost is measured. FIG. 5 shows the fraction of clay lost by weight m (%)as a function of time t (s). Curve 18 represents the test with asolution of H3.

By comparison, Curves 16 and 17 give the result of the same test with asolution of partially hydrolyzed polyacrylamide and with distilledwater, respectively. After a time of approximately 5,000 s, thedistilled water crumbles 40% of clay, the polyacrylamide solutioncrumbles 45%, and the solution containing H3 polymer, 20%.

It is clear that the combined action of the adsorption andhydrophobicity characteristics is determining for inhibiting theswelling and dispersion of argillaceous rocks by the polymers accordingto the invention.

Test 6

This test was conducted in the cell shown in FIG. 6. This cell simulatesa drilling well and allows circulation under pressure of a fluid in aborehole in a rock sample. In addition, a calibration probe continuouslymeasures the diameter of the borehole. Rock sample 12 is placed in anenclosure 21 with an annular space 22 delimited by a stopper 23, ajacket 24, and the body of enclosure 21. Pump 25 applies a confinementpressure on sample 20. The sample has a borehole 26 which correspondswith orifice 27 in the enclosure and orifice 28 in cap 23. Thesepassages accommodate measuring probe 29 intended to measure the insidediameter of borehole 26. A circulation pump 30 causes test fluid tocirculate in borehole 26. A reservoir 31, a filter 32, and a pulsedamper 33 complete the experimental arrangement.

Sample 20 has a diameter of approximately 15 cm and is 20 cm long;borehole 26 is 2.54 cm in diameter.

The test is conducted at a confinement pressure of 260 bars and acirculation pressure of 250 bars for a flow rate of 12 l/min. The testslast approximately 48 hours.

The sample is a clay rock called "Stone I" containing approximately 50%clay. The sample was treated at a temperature of 150 bars to reduce itsactivity to approximately 0.9.

The results of the various tests performed with different fluids areshown in FIG. 7 where the horizontal axis represents time in hours andthe vertical axis, the mean diameter of borehole 26 in millimeters.

Curves 40a and 40b are for distilled water.

Curves 41a and 41b are for a solution containing partially hydrolyzedpolyacrylamides.

Curves 42a and 42b are for a solution containing H3.

Curves 43a and 43b are for a solution containing H6.

Indices a and b correspond to average measurements of the diameter ofborehole 26 along four orthogonal directions.

It is clear that the distilled water completely destabilizes the sample.Decreases and widenings of the hole diameter are clearly observed.

Polyacrylamide (41a, 41b) somewhat stabilizes the borehole walls butdoes not inhibit swelling of the clay rock. Indeed, the boreholediameter is substantially reduced.

Polymer H3 has very good stabilization and inhibition. The boreholediameter is regular and very close to the initial situation.

By contrast, the H6 polymer causes very severe destabilization of thesample even in the first hours of circulation. It was also found thatthe H6 polymer is adsorbed by a two-stage mode bringing about formationof a layer of the multilayer type at the surface of the clay sample.When circulation is established on the sample, some of the molecules inthe multilayer-type layer are no longer held at the sample surface, butentrained and recirculated. The layer thickness is then reducedsubstantially to the condition of a monolayer. The monolayer, about 0.2microns thick, does not inhibit swelling sufficiently because inparticular it does not effectively limit water diffusion.

By optimizing the structure and molecular weight of the polymer, anadsorbed layer thickness greater than 0.4 micron with sufficient densityto limit water diffusion can be reached.

These results are confirmed and explained in FIG. 8 which shows on thehorizontal axis the distance 1 of the samples from the borehole axis inmillimeters and on the vertical axis the residual water content w ofthese samples.

Curves 44, 45, and 46 are for the test with distilled water,polyacrylamides, and the H3 polymer, respectively.

For a given distance from the borehole axis, it can be seen that theclay rock sample is significantly less hydrated by the water in asolution containing polymer H3.

It can be seen that the strong adsorption and strong hydrophobicity ofthe hydrophobic polymers strongly inhibit swelling of a clay formation.

It can be seen that, to optimize the polymers according to theinvention, the circulation tests according to Test 6 are an essentialsupplement to tests of the static type. The latter tests, of type 0 and1, do not show completely the action of the polymers according to thepresent invention.

We claim:
 1. A method for stabilizing argillaceous rocks containingreactive clays in the presence of water, wherein said argillaceous rocksare placed in contact with an aqueous solution containing a polymer withhydrophilic groups (Hy) and hydrophobic groups (Hb) so that the polymeris adsorbed by said argillaceous rocks, said groups being able toinhibit swelling of said argillaceous rocks characterized in that:thehydrophobic groups contain C₄ -C₃₀ alkyl groups, the molecularproportion of said hydrophobic groups is between 5 and 60%, said polymerhas the following structure: a structure b1) of the --(Hb)--(Hy)-- typewith a statistical distribution, said structure b1) being apolyacrylamide derivative resulting from copolymerization of anacrylamide with a hydrophobic comonomer, and wherein the hydrophilicgroup is an acrylamide or derivative thereof having at least one of thefollowing forms: N-alkylacrylamide, alkyl acrylate, N-substitutedacrylamide, or substituted acrylate, whose substituted part is anonionic surfactant, said hydrophobic unit having the following generalformula: ##STR13## wherein R₅ is H or CH₃ and Z₂ is COOR₇, COOR'₁, CONR₁R'₁ or CONR₁ R₇, R₇ being a nonionic surfactant composed of an alkylpolyoxyethylene chain R₁ being H, or a C₄ -C₃₀ alkyl, aryl or alkylarylradical and R'₁ being a C₄ -C₃₀ alkyl, aryl, or alkylaryl radical.
 2. Amethod for stabilizing argillaceous rocks containing reactive clays inthe presence of water, wherein said argillaceous rocks are placed incontact with an aqueous solution containing a polymer with hydrophilicgroups (Hy) and hydrophobic groups (Hb) so that the polymer is adsorbedby said argillaceous rocks, said groups being able to inhibit swellingof said argillaceous rocks characterized in that:the hydrophobic groupscontain C₄ -C₃₀ alkyl groups, the molecular proportion of saidhydrophobic groups is between 5 and 60%, said polymer has the followingstructure: a structure b1) of the --(Hb)--(Hy)-- type, said structureb1) being a polyacrylamide derivative resulting from copolymerization ofan acrylamide with a hydrophobic comonomer, and wherein the hydrophilicgroup is an acrylamide, with cationic units being introduced intoStructure b1), said units having the following general formula:##STR14## wherein R₆ is H or CH₃, Z₃ is (CH₂)_(n), COO(CH₂)_(n) orCONH(CH₂)_(n) with n being a number from 0 to 20, and Y is R₁ N⁺ R'₁ R₂wherein only one of the three radicals R₁, R'₁ and R₂ is H, C₁ -C₃₀alkyl, aryl or alkylaryl radical and the remaining radicals are each aC₁ -C₃₀ alkyl, aryl or alkylaryl radical.
 3. A method for stabilizingargillaceous rocks containing reactive clays in the presence of water,wherein said argillaceous rocks are placed in contact with an aqueoussolution containing a polymer with hydrophilic groups (Hy) andhydrophobic groups (Hb) so that the polymer is adsorbed by saidargillaceous rocks, said groups being able to inhibit swelling of saidargillaceous rocks characterized in that:the hydrophobic groups containC₄ -C₃₀ alkyl groups, the molecular proportion of said hydrophobicgroups is between 5 and 60%, said polymer has the following structure: astructure b1) of the --(Hb)--(Hy)-- type, said structure b1) being apolyacrylamide derivative resulting from copolymerization of anacrylamide with a hydrophobic comonomer, and wherein the hydrophilicgroup is an acrylamide or derivative in the form of acrylic acid,acrylate or sulfonate according to the following formula: ##STR15##wherein R₅ is H or CH₃ and Z₁ is COOH or CONH₂ or CONHR"₁, with R"₁being a C₁ -C₃₀ substituted alkyl-, aryl-, or alkylarylsulfonateradical.
 4. Method according to claim 3 characterized by the aqueoussolution having between 1 and 10 g/liter of hydrophilic and hydrophobicpolymer.
 5. Utilization of the method according to claim 4 with fluidscontacting reactive argillaceous formations, particularly fluids fordrilling, fracturing, well treatment, or assisted recovery.
 6. Drillingfluid characterized by comprising the solution defined in claim
 3. 7. Amethod according to claim 3, wherein the polymer has the structure b1,wherein the hydrophilic group is acrylamide.
 8. A method according toclaim 3, wherein R₅ is H and Z₁ is COOH.
 9. A method according to claim3, wherein R₅ is CH₃ and Z₁ is CONH₂.
 10. A method according to claim 3,wherein R₅ is CH₃ and Z₁ is CONHR"₁ wherein R"₁ is a C₁ -C₃₀ substitutedalkyl-, aryl- or alkylaryl-sulfonate radical.